I have had the A9 since it's release. Here's a quick head's-up:
First, it's significantly peppy for not having a hex-core. Yeah, it's running a Q-comm 6-series chip, but even for that, it has a snappy boot up and run speed.
Second, it's compact, but not 'tiny'. It's screen clarity is comparable to your iPhone, but even thinner. However, it's a bit slippery. A good composite silicon/polycarb case will serve you well to 'fix' that (and only costs about $9 US on Amazon!)
Third, the A9 is the ONLY phone currently able to use Q-Comm's 'Quick Charge 3' series of fast-charging. I tested it by running my phone down to 45% and, after only 45 mintes, was back to 93%! So you're less likely to need to carry a External battery. (Though I do have that, too, and even then it only uses 1/4 of a 15000 mAh battery plugged in the whole 8 hours at work.)
Finally, it has a current-gen capacity for microSD, topping out theoretically at 2Tb. So, Just slot in a 128Gb or 256Gb card and go to town!
My only downside? The face 'protrudes' from the frame, so it will shatter easier. Again, get a composite case and that will reduce the danger to the glass.